The CUAV C-RTK 9P Receiver is an RTK GPS module designed by CUAV for the professional market. It uses Ublox’s F9P module, supports multi-satellite multi-frequency, and uses advanced RTK algorithms. It can build an RTK system with two identical C-RTK 9P modules. Using it, the PX4 can achieve centimeter-accurate position in seconds, which is much more accurate than the average GPS, and faster and more convenient than the previous generation M8P module.

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Key Features

• Receiver type
  • RTK Receiver: Ublox F9P
• GNSS
  • GPS / QZSS,Beidou,Galileo, GLONASS
• GNSS Bands
  • GPS L1C/A L2C, GLONASS L1OF L2OF, GALILEO E1B/C E5b, BDS B1I B2I, QZSS L1C/A L2C
• Nav. update rate
  • RTK Up to 20HZ
• Position accuracy
  • RTK 0.01 m + 1 ppm CEP
• Convergence time
  • RTK < 10 sec
• Acquisition
  • Cold starts 24 s
  • Aided starts 2 s
  • Reacquisition 2 s
• Sensitivity
  • Tracking & Nav –167 dBm
  • Cold starts –148 dBm
  • Hot starts –157 dBm
  • Reacquisition –160 dBm
• Anti-jamming
  • Active CW detection and removal Onboard band pass flter
• Anti-spoofng
  • Advanced anti-spoofng algorithms
• Interfaces
  • 2 UART
  • 1 USB
  • 1 I2C
  • 1 Antenna interface(MMCX)
• Protocols
  • NMEA
  • UBX binary
  • RTCM version 3.x
• Supply voltage
  • –40 °C to +85 °C
• Size
  • 31.5*48*12MM
• weight:21g

Hardware connection

Base station Hardware connection

• The base station is connected to the computer usb interface through the type c cable; the telemetry is connected to another usb interface of the computer.

When using, please place the base station outdoors with enough sky coverage to get a good search signal. Place the base station on a stable and elevated platform, such as a tripod.

Rover Hardware connection

connection to V5+ or V5 nano

• Please use V5+ or V5 nano special cable 10 pin connector plugged into GPS&SAFETY PORT, 6 pin connector plugged into UART 4.
• Telemetry: Connect to the TELEM(radio) interface

connection to Pixhack

Please use pixhack special cable

• Six wire connector plugged into GPS&SAFETY PORT, Four wire connector plugged into UART 4.
• Telemetry: Connect to the TELEM(radio) interface.
  

  Pinouts

If you are connected to other flight controller, select the C-RTK 9P (for V5+) kit, which contains wires that connect to other PX4 flight controls(it can be used to connect Pixhawk3 pro or other flight controls, normally you do not need to Modify the wire).

The following interface description is C-RTK Cable (for V5+ or V5 nano)

C-RTK 9P User guide(for ArduPilot)

This tutorial uses the Mission Planner ground station software and the Arducopter-3.5 firmware. If you are using PX4 firmware and QGroundControl ground station software,Please read the PX4 RTK docs.

Please prepare the following hardware devices and perform hardware connection before use.

Base station configuration

This is not necessary if you use C-RTK BASE.

If you use Ardupilot firmware to build an RTK differential system, you need to perform base station-side positioning configuration and data forwarding through the missionplanner. During the positioning configuration of the base station, there is no need to start the mobile station and drone.

• Open the Mission Planner
• Enter the initial settings
• Click on optional hardware
• Click on RTK/GPS Inject you will see the following page:

• Set the base station port in the upper left corner
• Click connect
• In the SurveyIn Acc section, enter the absolute geographic accuracy that you expect your C-RTK base station to achieve. In the Time field, enter the shortest search time you want.
• Click Restart (the ground station will transfer the data you input to the C-RTK 9P base station, and the base station will start a new round of search star positioning)
• You will see the following page: During the search process, the current search star positioning will be displayed in the box on the right side of the Mission Planner page:

• Position is invalid: The base station has not yet reached a valid location;
• In Progress: Search Star is still in progress;
• Duration: The number of seconds the current search star has been executed;
• Observation: the number of observations obtained;
• Current Acc: The absolute geographic accuracy that the current base station can achieve.
• The green bars below the Mission Planner show the satellite and satellite signal strengths that the current base station has searched for. In an ideal environment, the C-RTK 9p can have an absolute accuracy of 2.5m in a matter of seconds. If you need higher absolute accuracy, it may take a long time.

The absolute geographic accuracy of the base station here will affect the absolute geographic accuracy of the mobile station without affecting the relative accuracy of the base station and the mobile station. If your application does not require drones with high absolute geographic accuracy, you don’t need to set the base station’s accuracy too high, resulting in longer search times. Even if the accuracy of the base station is 1.5~2m, the positional accuracy of the mobile station relative to the base station can still reach the centimeter level.

After the C-RTK 9P base station search star is completed, the Mission Planner will display the following page:

The figure below shows that the indicator of the base station status is displayed in green, while the three satellite systems of GPS, Glonass and Beidou are displayed in green. The box on the right shows the status as Position is valid and displays the current latitude and longitude.

RTK positioning status

Using the paired digital transmission module to connect to the same Mission Planner ground station, the data of the base station will be transmitted to the C-RTK rover station on the drone through the data transmission module. On the main page of Mission Planner, you can see that the current GPS status of the drone is displayed as RTK Float/RTK Fixed/3D RTK, indicating that the UAV’s positioning has entered the RTK state.

• RTK Float is a floating point solution.
• RTK Fixed is a fixed solution.

RTK Fixed has higher accuracy and is extremely environmentally demanding, and positioning can enter the RTK Fixed state when the signal is good enough。

C_RTK 9P User guide(for PX4)

Real-time motion (RTK) increases the accuracy of GNSS / GPS systems to the centimeter level. RTK makes PX4 can be used for precision measurement and other precision measurement.

Please prepare the following hardware devices and perform hardware connection before use.

Data transmission

The aircraft must be connected to the ground station via data / communication links. The link must use the MAVLink2 protocol because it can use the channel more efficiently. This should be set by default, but if not, follow the MAVLink2 configuration instructions below.

C-RTK 9P connection process

RTK GPS connection is essentially plug and play:

• Start QGroundControl and connect the C-RTK 9P base station to the ground station via USB. The device is automatically identified.
• Start the vehicle and make sure it is connected to the QGroundControl.
• The QGroundControl initiates the RTK setup process (called “entering a survey”).
• The entry survey is the start-up procedure to get an accurate estimate of the location of the base station. This process usually takes a few minutes (ending when the minimum time and accuracy specified in the RTK settings are reached). You can track progress by clicking the C-RTK GPS status icon.

Note: When the C-RTK GPS device is connected (except for the normal GPS status icon), the C-RTK GPS status icon will be displayed in the top icon bar. When RTK is set, the icon is red, and once the RTK GPS is in the survey complete state, the icon will turn white.

You can click the icon to see the current status and RTK accuracy.

Once the survey is completed:

The C-RTK GPS icon turns white and QGroundControl begins transmitting position data to the aircraft:

Aircraft GPS switched to RTK mode. The new mode is displayed in the normal GPS status icon (3D RTK GPS lock):

Optional PX4 configuration

The following settings may need to be changed (using QGroundControl)

C-RTK GPS 9P set up

C-RTK 9P GPS Settings Specified in QGroundControl General Settings (SettingsView & gt; General Settings)

These settings define the minimum duration and minimum accuracy (referred to as “measurement input”) to complete the C-RTK GPS setup process.

MAVLink2

The MAVLink2 protocol must be used because it can use lower bandwidth channels more efficiently. This should be enabled by default in recent builds.

To make sure MAVLink2 is used:

Update telemetry module firmware to the latest version（Please refer to QGroundControl>seting >firmware）.

Set MAV_PROTO_VER to 2（Please refer toQGroundControl seting >parameter）

debugging

You may also need to adjust some of the parameters, because the default parameters are adjusted in meters instead of centimeters. For example, you can reduce EKF2 _GPS_V_NOISE and EKF2_GPS_P_NOISE to 0.2.